Production of fibers of improved elastic recovery



July 11, 1967 J. D. TESSIER 3,330,897

PRODUCTION OF FIBERS OF IMPROVED ELASTIC RECOVERY Original Filed Oct. 1. 1964 2 Sheets-Shet 1 INVENTOR Joseph D. L. TESSIER ATTORNEY July 11. 96 J. D. L. TESSIER 3,

PRODUCTION OF FIBERS OF IMPROVED ELASTIC RECOVERY Original Filed Oct. 1, 1964 2 Sheets-Sheet 2 A B Cb 2 0 40 6 0 80 IOEE Ex TENS/OA/(Z) l I ga INVENTOR Joseph D. L. TESSIER ATTORNEY United States Patent Claims priority, application Great Britain, Feb. 7, 1961, 4,596/ 61, Patent 962,231 7 Claims. (Cl. 264-176) This application is a continuation of application Ser. No. 400,751, filed Oct. 1, 1964 and now abandoned which in turn is a continuation-in-part of application Ser. No. 171,568, filed Feb. 7, 1962, now abandoned.

This invention relates to the production of fibers of improved elastic recovery. More specifically, this invention relates to fibers of improved elastic recovery made from polyolefins, and to their method of production.

Wool, polyester and polyamide fibers have a very high elastic recovery. Thus, the fiber of products made from any one of these materials, after being stretched to a limited extent, will return substantially to its original length. This property is of great importance in garment manufacture where good elastic recovery is responsible for the garments retaining their shape and remaining free from Wrinkles over long periods. It is also of importance in all kinds of fabrics which are subjected in wear to considerable stretch as for example, in automobile seat covers.

Synthetic fibers have been produced from polypropylene and other polyolefins that show a fairly complete elastic recovery from a 10 and up to extension. These fibers will usually break when stretched to more than -50% of their original length. Some polyolefin fibers, produced by other prior art methods, can be stretched to an even higher percentage of their original length without breaking but these fibers, upon stretching, will take a high permanent deformation.

It has now been found, in accordance with the present invention, that polyolefin fibers produced by the process of the present invention have an elastic recovery of 85 to 100% when stretched to from 35 to 100% of their original length. Moreover, these fibers can be stretched to as high as 500% of their original length without breakmg.

It is an object of the present invention to prepare polyolefin fibers having a nearly complete elastic recovery from a very high extension. It is another object of the present invention to prepare polypropylene fibers, and especially those consisting prevailingly of isotactic polypropylene, having a nearly complete elastic recovery from a very high extension.

According to the present invention, the elastic recovery of such fibers from high extension is improved by subjecting them to a heat treatment without practically stretching the fiber and preferably under such conditions that shrinkage can occur.

The present invention thus consists in a process for the production of polyolefin fibers having a nearly complete elastic recovery from a high extension, said process comprising subjecting polyolefin filaments having a birefringence of 0008-0020 to a heat treatment without stretching at a temperature below the melting point thereof and above 85 C. for a period of time sufiicient to produce a fiber having an elastic recovery of 85 to 100% when stretched to from 35% to 100% of its original length. The birefringence of the fiber does not change to any substantial extent during the heat treatment.

The polyolefin filaments are preferably prepared by spinning polyolefin fibers from a melt while applying a 3,330,897 Patented July 11, 1957 ice draw-down t0 the filaments from the spinning jet of more than 10 times, preferably more than 20 times.

A preferred polyolefin for treatment according to the present invention is polypropylene consisting prevailingly of isotactic polypropylene having a melting point of about 160 to 165 C. The degree of isotacticity of polypropylene is not very critical, though it is desirable that the polymer should be at least 70% isotactic.

In a preferred embodiment of thepresent invention, the polyolefin fibers are subjected to the aforesaid heat treatment under such conditions that shrinkage can ocour.

The present invention further consists in synthetic polyolefin fibers having an almost complete elastic recovery from a high elongation and produced as hereinbefore described, and more specifically, in synthetic polyolefin fibers having an elastic recovery of about 100%, when stretched from 35% to of their original length.

In the present specification and claims, the term fiber is used, whenever the context permits, to include both continuous filament and staple fiber. Some fibers having a tendency to soften at a somewhat lower temperature than their melting point, the term melting point is used throughout the specification and claims unless the context indicates otherwise, as the temperature at which the fiber softens or melts, whichever occurs first.

The heat treatment may be carried out with the fiber, continuous filaments or cut staple fiber in the loose state, for example, in an oven heated to the appropriate temperature. Alternatively, where the time of treatment is sufficiently short, the heat treatment may be applied in a continuous run of the yarn or bundle of filaments; when the fiber is not heat treated in a continuous manner, adequate times of treatment include from 2 to 10 minutes. Such heat treatment may be by means of hot air, e.g. in a jacketed tube, by infra-red rays, by dielectric heating or by direct contact of the running yarn or bundle with a heated metal surface, preferably curved to make good contact. The yarn or bundle may be under just sufiicient tension to prevent shrinkage but preferably is allowed to shrink by a predetermined amount, for example, by 5 to 15% of its original length.

The fiber, before treatment, can be at room temperature. In such a case, the heating time required will considerably be extended, i.e. by the time required for the fiber to reach the desired temperature for the heat treatment.

Temperatures approaching the melting point of the fiber appear to give the greatest increase in elastic recovery but lower temperatures may be used. Generally, with all the synthetic polymer fibers, the heat treatment is carried out at a temperature in the range of 85 C. to the melting point of the polymer preferably between 100 C. and 10 to 15 below the melting point of the polymer.

Preferred polyolefins for treatment according to the invention are isotactic polypropylene, poly-3-methyl butene, and other poly-0c olefins, for example poly-4-methyl pentene. Preferred fibers for treatment according to the invention also include polyacetal resins.

Polypropylene fibers consisting prevailingly of isotactic polypropylene (e.g. 7085%) respond particularly well to the heat treatment. The elastic qualities of polypropylene fibers consisting prevailingly of isotactic polypropylene are improved very markedly by a heat treatment at a temperature from 85 C. up to the melting or softening point of the polymer. A period of heating of two minutes at C. produced a very pronounced in.- crease in elastic recovery and this was still further improved by extending the heating time at this temperature to 4 minutes and even to 10 minutes, but there appeared to be little advantage in further extending the heating time. The same considerations as to heating time apply when heating is carried out at 100 C. at which temmrature the increase in elastic recovery is not so great. The above heating times refer to polypropylene fibers which had previously been preheated to the temperature desired for the heat treatment. In such a case, the preheating time can vary considerably, according to the amount of fiber being preheated and the method used for preheating the fiber. For example, in a specific case, a bundle containing 1 lb. of isotactic polypropylene was preheated in an oven and it required 30 minutes for the fibers at the center of the bundle to reach the treatment temperature. On the other hand, if the same fiber is heat treated in a continuous run of the yarn, the required temperature would be reached in only a few minutes.

Normally synthetic polymer fibers are spun from a melt of the polymer, the filaments being subjected to a drawndown from the jet, and subsequently are stretched, e.g. to 3 to 5 times their length to increase their tenacity and decrease their extension at break. It is preferable in accordance with the present invention to omit the stretching step altogether but to apply an increased draw-down from the spinning jet, the maximum draw-down being dependent on the drawing properties of the particular molten polymer.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

FIGURE 1 illustrates in schematic form a preferred embodiment of the process of the present invention and,

FIGURE 2 illustrates a curve showing the extension and recovery of a polypropylene yarn in relation to the amounts of stress to which the yarn has been subjected.

With reference to FIGURE 1, polypropylene filaments are melt-extruded through nozzle of a conventional spinning jet. These filaments are gathered together While being air-cooled, then passed around guiding roll 30, then through heating oven 40. The yarn coming out of the heating oven is passed through feed rolls 50, and thence to take-up device 60. The speeds of extrusion and of feed rolls are controlled to obtain a drawdown of more than 10 times while not stretching the yarn during its passage through the oven.

The invention will now be described in more detail with reference to the following non-limiting examples.

EXAMPLE 1 A yarn of filaments and 900 total denier was produced by extruding isotactic polypropylene containing small amounts of light stabilizer (sold under the trademark Pro-fax by Hercules Powder Co.) having a tenacity of 1.3 g./d. under a tension corresponding to a take-up speed of yards/minute. The yarn thus produced, having a birefringence of 0.0125, was spread on a fine metallic screen and placed in a hot air oven heated to C. for 10 minutes.

The yarn was then subjected to a 100% elongation in the following manner: 10 inch yarns were stretched at room temperature from an original length of 10 inches to a final length of 20 inches and were then released.

The cycle was repeated by subjecting the same yarn to the same amount of stretching after it had recovered.

The results are shown in FIGURE 2 of the drawings in which the extension and recovery of the yarn are plotted in relation to the stress to which the yarn had been subjected.

In FIGURE 2, curve 1A shows the extension curve of the yarn up to 100% extension on the first cycle. The yarn was then released and recovery was as shown in curve 13. Recovery was about 90% as measured by the ratio of the distance CE to the distance AE as measured on the Extension coordinate.

Curve 2A shows the extension curve of the yarn on its second cycle. The yarn was again stretched as shown by curve 2A to 100% elongation, based on its original length. Curve 2B shows the elastic recovery of the yarn on release.

4 Recovery was even better on this cycle than on the first, as measured by the ratio of the distance DE to the distance BE on the extension coordinate.

EXAMPLE 2 A yarn of 150 filaments and 1200 total denier was produced by extruding 85 isotactic polypropylene containing a small amount of light stabilizer by conventional methods under a tension equal to the tension required to form the yarn as it was extruded. The yarn thus produced was spread on a fine metallic screen and placed in a hot air oven heated to C. Qualitative handtests showed marked improvement in elastic recovery after only 2 minutes and still further improvement after 10 minutes. The trial was terminated after 40 minutes but no further improvement was noted after 10 minutes. The filaments were stretched by 35% of this length without breakage and on release of tension, recovered over 99% of the extension imposed on this second cycle.

EXAMPLE 3 Seven samples of yarn consisting of 85 isotactic propylene and obtained in the same manner as in Example 2 except as hereinafter noted were compared for elastic recovery. Six of these samples had been subjected to a heat treatment in the same conditions as for Example 1 except as hereinafter noted. The other sample was not subjected to any heat treatment.

The results were as follows:

Sample 1. Untreated Very poor elastic recovery. Sample 2.. Heat treated at 50 C. Same as Sample 17 Sample 3. Heat treated at 85 C! Improved elastic recovery. Sample 4.. Heat treated at 100 C. for Marked improvement in elastic recovery. Substantially same as Sam- 10 minv Sample 5.. Heatl treated at 100 C. for

15 us. ple 4.

Sample 6. Heat treated at 145 C. for Substantially same as Sam- 10 min. ple 4.

Sample 7.. Heat treated at 145 C. for Substantially same as Sam 40 min. ple 4.

l No improvement occurred when the time of heating was extended. 1 A small improvement, over the elastic recovery shown by Sample 3 was noted when the time of heating was extended.

EXAMPLE 4 EXAMPLE 5 A yarn of 75 filaments, 3700 total denier and having a birefringence of 0.0153 was produced by extruding predominantly isotactic polypropylene (sold under the trade mark Pro-fax, Grade 6501, by Hercules Powder Co.) containing a small amount of light stabilizer by conventional spinning under a filament tension of 24 mg./ den. The yarn thus produced was treated as described in Example 4. The yarn obtained showed an immediate elastic recovery of 94% when stretched to 50% elongation.

It has already been stated that the process of the present invention is applicable to polyolefin fibers. It is also applicable to polyacetal resins which also show a remarkable elastic recovery, although somewhat less than polyolefins. However, polyacetal resins will also show, after treatment in accordance with the invention, an elastic recovery of 85-100% when stretched to from 35 to 50% of their original length.

I claim:

1. A process for the production of polypropylene fibers, said fibers having an elastic recovery of at least 85% when stretched to of their original length and an elongation at break of at least 100%, said process comprising melt spinning polypropylene while drawing down into fibers and subjecting said fibers to a heat treatment under non-stretching conditions at a temperature below the melting point thereof and above C., for a period of time sufiicient to produce said fibers having said elastic recovery.

2. A process, as claimed in claim 1, in which shrinkage of the fibers occurs during the heat treatment.

3. A process, as claimed in claim 1, in which said polypropylene is predominantly isotactic polypropylene.

4. A process, as claimed in claim 3, in which the heat treatment is carried out at a temperature of from to C.

5. A process as claimed in claim 1 wherein said fibers have been obtained by spinning into filaments from a melt while applying a draw-down'to the filaments from the pinning jet of more than 10 times.

6. A process as claimed in claim 5, wherein said period of time is at least 2 minutes.

7. A process as claimed in claim 1, wherein said elongation at break is between 100 to 500%.

References Cited UNITED STATES PATENTS 2,880,057 3/1959 Cuculo 264-178 3,054,652 9/1962 Heumann 264210 3,103,407 9/1963 Clark et al. 264290 3,106,442 10/1963 Compostella et a1. 264290 3,112,300 11/1963 Natta 260-93] 3,112,301 11/1963 Natta 26093.7 3,152,380 10/1964 Martin 264210 X 3,173,977 3/1965 Esselmann et al. 264210 3,233,023 2/1966 Benson 264--210 3,256,258 6/1966 Herrman 264-210 FOREIGN PATENTS 124,700 7/ 1947 Australia.

244,825 5 1963 Australia.

810,023 3/ 1959 Great Britain.

875,108 8/1961 Great Britain.

962,231 7/ 1964 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

J. H. WOO, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF POLYPROPYLENE FIBERS, SAID FIBERS HAVING AN ELASTIC RECOVERY OF AT LEAST 85% WHEN STRETCHED TO 35% OF THEIR ORIGINAL LENGTH AND AN ELONGATION AT BREAK OF AT LEAST 100%, SAID PROCESS COMPRISING MELT SPINNING POLYPROPYLENE WHILE DRAWING DOWN INTO FIBERS AND SUBJECTING SAID FIBERS TO A HEAT TREATMENT UNDER NON-STRETCHING CONDITIONS AT A TEMPERATURE BELOW THE MELTING POINT THEREOF AND ABOVE 85*C., FOR A PERIOD OF TIME SUFFICIENT TO PRODUCE SAID FIBERS HAVING SAID ELASTIC RECOVERY. 